Typical carburetors for internal combustion engines used in vehicles such as automobiles, aircraft, watercraft, motorcycles and small offroad sport vehicles, and powered devices such as chain saws, lawnmowers, garden equipment, generators, etc., include an air flow passageway having a shape that can be characterized as a venturi shape, that is a shape having a side wall therearound which defines larger cross-sectional end portions and a narrower intermediate portion or throat. This passageway or venturi can include a throttle plate located therein positionable at different angular orientations for regulating the flow of air therethrough, and also a choke plate movable in the same manner for facilitating cold starts. Fuel can be delivered to the venturi through one or more outlets or orifices located on the side wall and also through outlets on a tubular member in some constructions called a booster located in the central portion of the venturi in what is known as the free air stream. The free air stream is that portion of the air flow through the venturi which is not affected by any object in the air flow including the side wall of the venturi itself. The fuel is delivered to the orifice or orifices and to the booster by one or more fuel circuits communicating therewith. The fuel circuits can each include one or more fuel conduits or passageways communicating the orifices with fuel receiving and holding means.
Carburetors are typically of two kinds, one kind being characterized by having a fuel bowl, the delivery of fuel to which is controlled by a float mechanism which operates a fuel inlet valve. The second type is known as a diaphragm carburetor and can have one or more fuel chambers or cavities for holding fuel, the inlet valve regulating the delivery of fuel thereto being controlled by a diaphragm type member.
The fuel flow to the venturi in both float bowl and diaphragm type carburetors is largely dependent upon a pressure differential or pressure drop existing between the air flowing or passing through the venturi, and another pressure, usually atmospheric pressure present in another portion of the carburetor. The pressure in the venturi required to cause fuel flow is a negative pressure or partial vacuum condition produced by the operation of the engine drawing a flow of air from the atmosphere through the venturi. This partial vacuum condition, in turn, acts to draw the fuel through the fuel delivery orifices located in the booster and/or on the side wall of the venturi and into the venturi wherein the fuel mixes with the air and is drawn into the engine. In the float bowl type carburetor, as fuel is drawn from the bowl, the inlet valve opens to replace this fuel when the fuel level in the bowl falls to or below a certain predetermined level, as is well known in the art. In a diaphragm type carburetor, the negative pressure or partial vacuum condition from the venturi operates as a diaphragm activation signal. The diaphragm activation signal is communicated through one or more of the fuel passages to one side of the diaphragm, the opposite side of the diaphragm being typically in communication with atmospheric pressure. The pressure differential acting on the diaphragm causes deflection of the diaphragm towards the vacuum side to operate the inlet valve to cause fuel from the fuel supply to enter the fuel chamber, as is also well known in the art.
Under steady-state conditions, the above-described carburetor constructions provide generally satisfactory performance. However, under changing or dynamic conditions, such systems suffer from several significant shortcomings. For instance, when the throttle plate position is changed so as to provide for a greater flow of air through the venturi, this more open condition causes the partial vacuum condition in the venturi to weaken momentarily, reducing the vacuum signal and causing less, not more, fuel to be delivered to the venturi. This throttle change can also cause some of the atomized or emulsified fuel in suspension in the air stream flowing into the engine to fall out of suspension, resulting in poor combustion and a momentary performance lag from the engine and also increased engine smoking. This smoking problem is particularly noticeable in two cycle engines. The momentary reduction in vacuum signal also causes the activation of the diaphragm to be delayed so as not to react immediately to the greater fuel need, resulting in what is known as a lean shot of air to the engine, which is also undesirable.
Diaphragm type carburetors are sealed devices so as to enable operation at other than an upright or vertical orientation without leakage or spillage of fuel, and as such, do not have what is known as an air bleed system communicating with atmosphere as is typically found in float bowl type carburetors. This air bleed system can act as vacuum breaker or anti-siphon means under certain operating conditions. A shortcoming of diaphragm type carburetors which do not have an air bleed system is that when the throttle plate is suddenly closed, such as during sudden decceleration, without a vacuum break the vacuum signal increases substantially so as to flood the carburetor with fuel. This flooding can cause erratic performance in the operation of the engine known as stumbling and can even cause the engine to stall and die. Furthermore, this sudden vacuum signal increase can cause premature fatigue and reduce the effectivenesss of spring members associated with the inlet valve means of diaphragm carburetors, and can result in excessive wear of the valve seat and needle valve member. This resultant reduction in spring effectiveness and valve wear is especially problematic in multiple carburetor applications wherein the operation of the respective carburetors must be closely synchronized. This problem also makes the selection of jet sizes for the carburetors particularly critical.
Numerous solutions to the above-described vacuum signal related fuel delivery problems have been attempted, but with only limited success. For instance, one approach has been to compensate for erratic or poor vacuum signal by the use of accelerator pump means and the like, different jet sizes and by varying inlet valve spring constants, etc. Another approach has been to attempt to regulate the vacuum signal by the use of means such as an air flow restrictor located on the intake side of a carburetor to regulate intake pressure conditions. Another approach has been to locate one or more fuel delivery orifices so as to be responsive to vacuum conditions at different locations in the venturi and in the air stream therethrough, and so as to be responsive to different throttle plate positions. Still further, fuel injection systems have been used as an alternative fuel delivery means in an attempt to eliminate the above-described problems. However, fuel injection can add complexity and expense; it provides only marginally satisfactory results; and it can lead to additional problems.
In addition to the above-described fuel delivery problems relating to erratic and poor vacuum signal, the known prior art carburetor constructions have suffered from other numerous long standing problems. For instance, choke mechanisms required for cold starting add still further complexity to the carburetor and can be unreliable and require frequent adjustments. The emissions levels of engines aspirated using the known carburetor constructions can be unacceptably high, especially in view of increasing government regulations focusing on emissions. This is particularly problematic in regard to two cycle engines.
In contrast to the above-discussed attempted solutions and alternatives, the present invention provides simple, reliable and inexpensive means for solving the above-described problems which can be incorporated into new carburetor designs and, importantly can be retrofitted into existing carburetors. The present invention can also replace existing fuel delivery means, or it can be used in association therewith.